Senior C# Developer within FX Options – Investment Banking – Greenfield Project Location: Central London (3 days per week onsite) Contract Type: Outside IR35 Salary / Rate: Up to ~£825 / day DOE A leading investment banking team is embarking on a greenfield build of a high-performance pre-trade application and is seeking a Senior C# Developer with strong experience in Options (ideally FX Options) to join them at inception of the project. This is a rare opportunity to influence best practices from the ground up, working directly with the FX Options trading desk to design and build a system that handles large volumes of market data in near real-time. Key Responsibilities: Design and develop scalable, high-performance systems using modern C# .Net (version 9) Build and integrate APIs and microservices to support trading workflows Collaborate closely with FX Options traders to understand business requirements and deliver tailored solutions Contribute to architectural decisions and establish development standards for a greenfield application Participate in the migration of legacy monolithic systems to microservices (Optional) Support front-end development using ReactJS across related applications Required Experience: Expert-level proficiency in C# with a strong grasp of recent language features and .NET ecosystem Proven experience working with FX Options trading systems or directly with Options traders Solid understanding of systems integration, API design, and microservices architecture Experience handling large-scale market data in low-latency or real-time environments Hands-on experience converting monolithic applications into microservices Desirable: Exposure to ReactJS or willingness to contribute to front-end development when needed This role offers the chance to work on a high-impact, greenfield build in a fast-paced trading environment, with direct access to the business and the autonomy to shape technical direction.